High refractive index curable liquid light emitting diode encapsulant formulation

ABSTRACT

A curable liquid polysiloxane/TiO 2  composite for use as a light emitting diode encapsulant is provided, comprising: a polysiloxane prepolymer with TiO 2  domains having an average domain size of less than 5 nm, wherein the curable liquid polysiloxane/TiO 2  composite contains 20 to 60 mol % TiO 2  (based on total solids); wherein the curable liquid polysiloxane/TiO 2  composite exhibits a refractive index of &gt;1.61 to 1.7 and wherein the curable liquid polysiloxane/TiO 2  composite is a liquid at room temperature and atmospheric pressure. Also provided is a light emitting diode manufacturing assembly.

The present invention relates to a curable liquid polysiloxane/TiO₂composite comprising: a polysiloxane prepolymer with TiO₂ domains havingan average domain size of less than 5 nm; wherein the polysiloxaneprepolymer has an average compositional formula:(R⁴ ₃SiO_(1/2))_(a)(R¹(R²)SiO_(2/2))_(b)(R³SiO_(3/2))_(c)(R⁵_(x)Z_(y)SiO_((4-x-y)/2))_(d)wherein the curable liquid polysiloxane/TiO₂ composite contains 20 to 60mol % TiO₂ (based on total solids); wherein the curable liquidpolysiloxane/TiO₂ composite exhibits a refractive index of >1.61 to 1.7and wherein the curable liquid polysiloxane/TiO₂ composite is a liquidat room temperature and atmospheric pressure. The present inventionfurther relates to a light emitting diode manufacturing assembly.

A light emitting diode (LED) device typically comprises an LED die thatis encapsulated by an optically clear and thermally stable material. Theencapsulating material generally serves at least one of three functions,namely (1) it facilitates incorporation of the light emitting diode intoa device; (2) it provides protection for the fragile wiring for thelight emitting diode; and (3) it behaves as a refractive intermediarybetween the high index die and low index air. In some LED devices, apreformed plastic lens or glass lens is affixed or bonded to a packagein which the LED die is mounted. A curable liquid encapsulant materialis then injected into the cavity between the LED die and the plasticlens (or glass lens) and is subsequently cured to completely seal theLED die.

There is an increasing trend of directly molding a curable liquidencapsulant material onto an LED die using an in-line molding process.In these in-line molding processes, a curable liquid encapsulantmaterial is injected or potted into a mold cavity containing a LED die(or into which an LED die is immersed) and then curing the encapsulantmaterial, wherein the encapsulant material both encapsulates the LED dieand forms a lens for shaping the light emitted from the LED die. Suchin-line molding processes eliminate the prefabrication and assembly of alens into the LED device. As a result, such in-line molding processespromise more cost effective high volume manufacturing of LED devices.

Accordingly, high refractive index polymers are of interest as lens andencapsulant materials for use in light emitting diode deviceapplications. For example, in the manufacture of LED devices,manufacturers desire optical polymers with high transparency in thevisible region, high refractive indices (i.e., refractive indices ofapproximately 1.60 or higher), and excellent heat stability over tens ofthousands of hours of operation. The use of high refractive indexmaterials can considerably improve the light extraction efficiency froman LED die at the same drive current, hence making the LED device moreenergy efficient. Additionally the LED device industry uses liquidprepolymers, which are then cured in place after much of the device hasalready been assembled. Therefore the curing polymer system must showminimal shrinkage, and must be curable under conditions which do notharm the assembled device.

Materials conventionally used to encapsulate LED dies include epoxyresins and silicones. Conventional epoxy resins tend to exhibit poorlight stability (i.e., they tend to yellow over time) over timefollowing exposure to ultraviolet light or to elevated thermalconditions. This yellowing leads to a reduction in light output from aLED device over time. On the other hand, conventional silicones exhibitmuch better heat and light stability. As a result, silicones arebecoming the dominant encapsulant for use in LED devices. Conventionalsilicone encapsulants; however, exhibit refractive indices ranging from1.41 to 1.57 (measured at 550 nm). Moreover, it has proven difficult toachieve refractive indices of higher than about 1.6 (measured at 550 nm)without compromising other key performance properties such asflowability in the uncured state.

The refractive index of the encapsulant plays an important role indetermining how much light is extracted from the LED device. This is dueto total, or very high internal reflection of light as it passes fromthe solid-state high refractive index LED die to a low index polymermedium. Typical LED dies have refractive indices of approximately 2.5.Thus, there is great interest in obtaining silicone encapsulants havinghigher refractive indices, while maintaining flowability in the uncuredstate.

The refractive index of a polymer is determined by the molarrefractivities of its constituent groups. Commercial silicone monomersare predominantly combinations of aliphatic groups and phenyl groups.This effectively limits the refractive index in traditional curableliquid silicones to an upper end of 1.57 to 1.58. The refractive indexof poly(diphenylsiloxane) is 1.61, but it is a solid polymer. Since manyapplications require liquid prepolymers, it is necessary to blend lowerglass transition temperature (T_(g)) monomers with diphenylsiloxanemonomers in order to obtain a liquid, leading to a reduction in therefractive index of the blended material. This leads to an upper limiton the refractive index of 1.57 to 1.58, as mentioned.

Two approaches have been suggested for enhancing the refractive index ofsilicone polymers. One approach is to blend organopolysiloxane with arefractive index enhancer such as TiO₂. Another approach is to reactsilicone precursors with titanium alkoxides. Notwithstanding, therefractive index exhibited by such materials is lower than expectedbecause of inhomogeneity of the product produced and the composites aredifficult to process (i.e., they are inhomogenious and non-flowable).

One group of liquid prepolymers are disclosed by Conner et al. in UnitedStates Patent Application Publication No. 2009/0039313. Conner et al.disclose a (thio)phenoxyphenyl phenyl silane composition comprising a(thio)phenoxyphenyl phenyl silane having formula IPh²-Q-Ph¹-Si(Ph³)(OR)₂  (I)wherein: Ph¹ is a phenyl ring having Ph²-Q-, —Si(Ph³)(OR)₂ and fourhydrogen atoms as substituents; Ph²-Q is a (thio)phenoxy group where Ph²is phenyl and Q is selected from oxygen atom, sulfur atom, andcombinations thereof; Ph²-Q is in a position on the Ph¹ phenyl ringwhich is ortho-, meta-, or para-relative to the Si atom; Ph³ is phenyl;and R is independently selected from a hydrogen atom, a C₁₋₁₀hydrocarbon radical, and combinations thereof; wherein the C₁₋₁₀hydrocarbon radical is independently selected from: linear, branched, orcyclic C₁₋₁₀ alkyl; phenyl; substituted phenyl; arylalkyl; andcombinations thereof.

Notwithstanding, there remains a need for transparent high refractiveindex materials for use in the manufacture of light emitting diodes. Inparticular, there remains a need for light emitting diode encapsulantformulations having high refractive index, good thermal stability, andtransparency which are liquid, or which form curable compositions whichare liquid before curing, during some portion of curing, or both. Inmany cases, silicone composites are needed which can be cured intoelastomers. In these cases, it is convenient to have liquid siliconecomposite based precursors which can be crosslinked to form curedcompositions.

The present invention provides a curable liquid polysiloxane/TiO₂composite for use as a light emitting diode encapsulant, comprising(consisting essentially of): a polysiloxane prepolymer with TiO₂ domainshaving an average domain size of less than 5 nm (preferably asdetermined by transmission electron microscopy (TEM)); wherein thepolysiloxane prepolymer has an average compositional formula:(R⁴ ₃SiO_(1/2))_(a)(R¹(R²)SiO_(2/2))_(b)(R³SiO_(3/2))_(c)(R⁵_(x)Z_(y)SiO_((4-x-y)/2))_(d)wherein each R¹ and R³ is independently selected from a C₆₋₁₀ aryl groupand a C₇₋₂₀ alkylaryl group; wherein each R² is a phenoxyphenyl group;wherein each R⁴ is independently selected from a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group and a C₆₋₁₀ aryl group;wherein each R⁵ is independently selected from a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group, a C₆₋₁₀ aryl group and aphenoxyphenyl group; wherein each Z is independently selected from ahydroxyl group and a C₁₋₁₀ alkoxy group; wherein 0≦a≦0.005; wherein0.8495≦b≦0.9995; wherein 0.001≦c≦0.10; wherein 0≦d≦0.15; wherein thecurable liquid polysiloxane/TiO₂ composite contains 20 to 60 mol % TiO₂(based on total solids); wherein x is selected from 0, 1 and 2; whereiny is selected from 1, 2 and 3; wherein a+b+c+d=1; and, wherein thecurable liquid polysiloxane/TiO₂ composite exhibits a refractive indexof >1.61 to 1.7 and wherein the curable liquid polysiloxane/TiO₂composite is a liquid at room temperature and atmospheric pressure.

The present invention also provides a curable liquid polysiloxane/TiO₂composite, comprising: a polysiloxane prepolymer with TiO₂ domainshaving an average domain size of less than 5 nm (preferably asdetermined by transmission electron microscopy (TEM)); wherein thepolysiloxane prepolymer has an average compositional formula:(R⁴ ₃SiO_(1/2))_(a)(R¹(R²)SiO_(2/2))_(b)(R³SiO_(3/2))_(c)(R⁵_(x)Z_(y)SiO_((4-x-y)/2))_(d)wherein each R¹ and R³ is independently selected from a C₆₋₁₀ aryl groupand a C₇₋₂₀ alkylaryl group; wherein each R² is a phenoxyphenyl group;wherein each R⁴ is independently selected from a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group and a C₆₋₁₀ aryl group;wherein each R⁵ is independently selected from a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group, a C₆₋₁₀ aryl group and aphenoxyphenyl group; wherein each Z is independently selected from ahydroxyl group and a C₁₋₁₀ alkoxy group; wherein 0≦a≦0.005; wherein0.8495≦b≦0.9995; wherein 0.001≦c≦0.10; wherein 0≦d≦0.15; wherein thecurable liquid polysiloxane/TiO₂ composite contains 20 to 60 mol % TiO₂(based on total solids); wherein x is selected from 0, 1 and 2; whereiny is selected from 1, 2 and 3; wherein a+b+c+d=1; wherein the curableliquid polysiloxane/TiO₂ composite exhibits a refractive index of >1.61to 1.7; wherein the curable liquid polysiloxane/TiO₂ composite is aliquid at room temperature and atmospheric pressure; wherein the curableliquid polysiloxane/TiO₂ composite is prepared by: (a) combining in anaprotic solvent: (i) D units having a formula R¹(R²)Si(OR⁶)₂; (ii) Tunits having a formula R³Si(OR⁷)₃; (iii) optionally, M units having aformula R⁴ ₃SiOR⁸; and, (iv) optionally, Q units having a formulaSi(OR⁹)₄; wherein each R⁶, R⁷, R⁸ and R⁹ is independently selected froma hydrogen atom, a C₁₋₁₀ alkyl group, a C₇₋₁₀ arylalkyl group, a C₇₋₁₀alkylaryl group and a C₆₋₁₀ aryl group; (b) adding to the combination of(a) an acid in a miscible mixture of water and an alcohol to form areaction mixture; (c) allowing the reaction mixture to react; (d) addingan organo-titanate in an aprotic solvent to the reacted reaction mixtureof (c); (e) adding water to the product of (d); (f) heating the productof (e) and allowing it to react; and, (g) purifying the product of (f)to provide the curable liquid polysiloxane/TiO₂ composite.

The present invention also provides a light emitting diode manufacturingassembly, comprising: a support structure having a plurality ofindividual semiconductor light emitting diode dies; and, a mold having aplurality of cavities corresponding with the plurality of individualsemiconductor light emitting diode dies; wherein the plurality ofcavities is filled with a curable liquid polysiloxane/TiO₂ composite ofthe present invention; and wherein the support structure and the moldare oriented such that the plurality of individual semiconductor lightemitting diode dies are each at least partially immersed in the curableliquid polysiloxane/TiO₂ composite contained in the plurality ofcavities.

DETAILED DESCRIPTION

Siloxane polymers have established many uses in the electronicsindustry. For example, siloxane polymers have use as underfillformulations, protective coatings, potting agents, die bonding agents,encapsulants and as lenses for light emitting diodes. In manyapplications in the electronics industry; however, special requirementsare presented given the constraints involved that necessitate that thepolymer used be in a liquid curable form. That is, in many suchapplications (e.g., underfill and lens molding), a partially orcompletely closed space is filled with liquid curable material, which issubsequently cured. For example, in the manufacture of lenses for lightemitting diodes a closed mold is commonly used to form the lens. Theliquid curable material is dispensed or injected into the mold cavityand then cured. In such molding processes, it is desirable to minimizethe content of volatiles in the liquid curable material used to avoidthe need to facilitate off gassing or the removal solvent from thesystem.

The curable liquid polysiloxane/TiO₂ composite of the present inventionis designed to facilitate the manufacture of light emitting diodeshaving a semiconductor light emitting diode die (preferably a pluralityof semiconductor light emitting diode dies), wherein the semiconductorlight emitting diode die(s) is(are) at least partially encapsulated(preferably, completely encapsulated) within the curable liquidpolysiloxane/TiO₂ composite. Specifically, the curable liquidpolysiloxane/TiO₂ composite of the present invention is surprisinglyliquid despite the high TiO₂ loading with minimal (<4 wt %, preferably<2.5 wt %) or no solvent (i.e., neat). The curable liquidpolysiloxane/TiO₂ composite of the present invention also exhibits ahigh refractive index (>1.61). These properties of the curable liquidpolysiloxane/TiO₂ composite of the present invention make it ideallysuitable for use in the manufacture of semiconductor light emittingdiodes.

The curable liquid polysiloxane/TiO₂ composite of the present inventionis curable using well known methods. Preferably, the curable liquidpolysiloxane/TiO₂ composite is thermally curable (preferably uponheating at 100 to 200° C. for 10 to 120 minutes).

The curable liquid polysiloxane/TiO₂ composite of the present invention,comprises (preferably consists essentially of): a polysiloxaneprepolymer with TiO₂ domains having an average domain size of less than5 nm (preferably ≦3 nm) as determined by transmission electronmicroscopy (TEM); wherein the polysiloxane prepolymer has an averagecompositional formula:(R⁴ ₃SiO_(1/2))_(a)(R¹(R²)SiO_(2/2))_(b)(R³SiO_(3/2))_(c)(R⁵_(x)Z_(y)SiO_((4-x-y)/2))_(d)wherein each R¹ and R³ is independently selected from a C₆₋₁₀ aryl groupand a C₇₋₂₀ alkylaryl group (preferably both R¹ and R³ are phenylgroups); wherein each R² is a phenoxyphenyl group, wherein thephenoxyphenyl group is bound with the silicon to form at least one ofthree different isomers, namely an ortho-phenoxyphenyl silane group, ameta-phenoxyphenyl silane group, or a para-phenoxyphenyl silane group;wherein each R⁴ is independently selected from a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group and a C₆₋₁₀ aryl group(preferably a C₁₋₅alkyl group, a C₇₋₁₀ arylalkyl group, a C₇₋₁₀alkylaryl group and a phenyl group; more preferably a C₁₋₅alkyl groupand a phenyl group; most preferably a methyl group and a phenyl group);wherein each R⁵ is independently selected from a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group, a C₆₋₁₀ aryl group and aphenoxyphenyl group (preferably a C₁₋₅alkyl group, a C₇₋₁₀ arylalkylgroup, a C₇₋₁₀ alkylaryl group, a phenyl group and a phenoxyphenylgroup; more preferably a C₁₋₅alkyl group, a phenyl group and aphenoxyphenyl group; most preferably a methyl group, a phenyl group anda phenoxyphenyl group); wherein each Z is independently selected from ahydroxyl group and a C₁₋₁₀ alkoxy group (preferably a hydroxyl group anda C₁₋₄ alkoxy group, more preferably a hydroxyl group and a C₁₋₂ alkoxygroup); wherein 0≦a≦0.005; wherein 0.8495≦b≦0.9995 (preferably0.9≦b≦0.9995, more preferably 0.9≦b≦0.9992, most preferably0.95≦b≦0.9992); wherein 0.0005≦c≦0.10 (preferably 0.0008≦c≦0.10, morepreferably 0.001≦c≦0.06, most preferably 0.001≦c≦0.02); wherein 0≦d≦0.15(preferably 0≦d≦0.099, more preferably 0≦d≦0.04, most preferably0.0005≦d≦0.02); wherein the curable liquid polysiloxane/TiO₂ compositecontains 20 to 60 mol % TiO₂ (based on total solids) (preferably 20 to58 mol %, more preferably 30 to 58 mol %, most preferably 50 to 58 mol%); wherein each x is independently selected from 0, 1 and 2 (i.e., xcan be the same or different for each Rx Z_(y)SiO_((4-x-y)/2) groupcontained in the prepolymer); wherein each y is independently selectedfrom 1, 2 and 3 (i.e., y can be the same or different for each R⁵_(x)Z_(y)SiO_((4-x-y)/2) group contained in the prepolymer); whereina+b+c+d=1; and, wherein the curable liquid polysiloxane/TiO₂ compositeis a liquid at room temperature and atmospheric pressure. Preferably,the curable liquid polysiloxane/TiO₂ composite of the present inventionexhibits a refractive index of >1.61 to 1.7, more preferably 1.63 to1.66, most preferably 1.64 to 1.66. Preferably, the curable liquidpolysiloxane/TiO₂ composite of the present invention exhibits aviscosity of <600,000 Pa*s, more preferably 4 to 100,000 Pa*s, mostpreferably 4 to 20,000 Pa*s measured under the conditions set forth inthe Examples. Preferably, the curable liquid polysiloxane/TiO₂ compositeof the present invention is thermally curable, optionally with theaddition of a catalyst.

Preferably, the curable liquid polysiloxane/TiO₂ composite of thepresent invention is prepared by: (a) combining in an aprotic solvent:(i) D units having a formula R¹(R²)Si(OR⁶)₂ (preferably 84.95 to 99.95mol %, more preferably 90 to 99.95 mol %, still more preferably 90 to99.92 mol %, most preferably 95 to 99.92 mol % D units); (ii) T unitshaving a formula R³Si(OR⁷)₃ (preferably 0.05 to 10 mol %, morepreferably 0.08 to 10 mol %, still more preferably 0.1 to 6 mol %, mostpreferably 0.1 to 2 mol % T units); (iii) optionally, M units having aformula R⁴ ₃SiOR⁸ (preferably 0 to 0.5 mol % M units); and, (iv)optionally, Q units having a formula Si(OR⁹)₄ (preferably 0 to 15 mol %,more preferably 0 to 9.9 mol %, still more preferably 0 to 4 mol %, mostpreferably 0.05 to 2 mol % Q units), wherein each R¹ and R³ isindependently selected from a C₆₋₁₀ aryl group and a C₇₋₂₀ alkylarylgroup (preferably both R¹ and R³ are phenyl groups); wherein each R² isa phenoxyphenyl group, wherein the phenoxyphenyl group is bond with thesilicon to form at least one of three different isomers, namely anortho-phenoxyphenyl silane group, a meta-phenoxyphenyl silane group, ora para-phenoxyphenyl silane group; wherein each R⁴ is independentlyselected from a C₁₋₁₀ alkyl group, a C₇₋₁₀ arylalkyl group, a C₇₋₁₀alkylaryl group and a C₆₋₁₀ aryl group (preferably a C₁₋₅ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group and a phenyl group; morepreferably a C₁₋₅ alkyl group and a phenyl group; most preferably amethyl group and a phenyl group); wherein each R⁶, R⁷, R⁸ and R⁹ isindependently selected from a hydrogen atom, a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group and a C₆₋₁₀ aryl group(preferably a hydrogen and a C₁₋₅ alkyl group; more preferably ahydrogen and a methyl group; most preferably a methyl group); (b) addingto the combination of (a) an acid (preferably a mineral acid; morepreferably a mineral acid selected from hydrochloric acid, nitric acid,phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid andhydrobromic acid; still more preferably a mineral acid selected fromhydrochloric acid, nitric acid and sulfuric acid; most preferablyhydrochloric acid) in a miscible mixture of water and an alcohol(preferably a C₁₋₈ alkyl hydroxide, more preferably methanol, ethanol,propanol, butanol) to form a reaction mixture (preferably, by adrop-wise addition, more preferably by a dropwise addition whilemaintaining the temperature at 0 to 80° C., most preferably by adropwise addition while maintaining the temperature at 15 to 70° C.);(c) allowing the reaction mixture to react (preferably, whilemaintaining the reaction mixture at a temperature of 0 to 80° C.; morepreferably, while maintaining the reaction mixture at a temperature of15 to 70° C.); (d) adding an organo-titanate in an aprotic solvent tothe reacted reaction mixture of (c) (preferably by a dropwise addition,more preferably by a dropwise addition while maintaining the temperatureat 30 to 100° C., most preferably by a dropwise addition whilemaintaining the temperature at 70° C.); (e) adding water to the productof (d) (preferably by a dropwise addition, more preferably by a dropwiseaddition while maintaining the temperature at 30 to 100° C., mostpreferably by a dropwise addition while maintaining the temperature at70° C.); (f) heating the product of (e) and allowing it to react to formthe curable liquid polysiloxane/TiO₂ composite (preferably, the productof (e) is heated to a temperature of ≧60°, more preferably 60 to 150°C.); and, (g) purifying the product of (f) to provide the curable liquidpolysiloxane/TiO₂ composite (preferably, wherein the curable liquidpolysiloxane/TiO₂ composite contains 20 to 60 mol % TiO₂ (based on totalsolids)).

The formation of the curable liquid polysiloxane/TiO₂ composite in (f)also results in the formation of by-products such as ethanol, methanol,isopropanol and water. These by-products are advantageously removed fromthe curable liquid polysiloxane/TiO₂ composite in (g). Preferably, theseby-products are removed from the curable liquid polysiloxane/TiO₂composite in (g) by at least one of distillation and roto-evaporation.Optionally, an extraction solvent can be used to aid in the removal ofthese by-products. Examples of extraction solvents include C₅₋₁₂ linear,branched and cyclic alkanes (e.g., hexane, heptane and cyclohexane);ethers (e.g., tetrahydrofuran, dioxane, ethylene glycol diether etherand ethylene glycol dimethyl ether); ketones (e.g., methyl isobutylketone, methyl ethyl ketone and cyclohexanone); esters (e.g., butylacetate, ethyl lactate and propylene glycol methyl ether acetate);halogenated solvents (e.g., trichloroethane, bromobenzene andchlorobenzene); silicone solvents (e.g., octamethylcyclotetrasiloxaneand decamethylcyclopentasiloxane); and combinations thereof.

Preferably, the D units used in the preparation of the curable liquidpolysiloxane/TiO₂ composite have a formula

wherein each R⁶ is independently selected from hydrogen and a C₁₋₄ alkylgroup (more preferably, wherein each R⁶ is a methyl group).

Preferably, the T units used in the preparation of the curable liquidpolysiloxane/TiO₂ composite have a formula

wherein each R⁷ is independently selected from hydrogen and a C₁₋₄ alkylgroup (more preferably, wherein each R⁷ is a methyl group.

Preferably, the acid used in the preparation of the curable liquidpolysiloxane/TiO₂ composite is selected from Brönsted acids (e.g.,acetic acid, formic acid, propionic acid, citric acid, hydrochloricacid, sulfuric acid and phosphoric acid). More preferably, the acid usedis selected from acetic acid and hydrochloric acid. Most preferably, theacid used is hydrochloric acid.

Preferably, the organo-titanate used in the preparation of the curableliquid polysiloxane/TiO₂ composite is selected from organo-titanatesaccording to the formula (R¹⁰O)_(e)Ti_(f)O_((f−1)); wherein each R¹⁰ isindependently selected from a C₁₋₂₀ alkyl group, a C₆₋₁₀ aryl group, aC₇₋₂₀ alkylaryl group and a C₇₋₂₀ arylalkyl group; wherein f is selectedfrom 1, 2, 3, 4 and 5; and wherein e=2*(f+1). More preferably, theorgano-titanate is selected from tetraethyl titanate; tetraisopropyltitanate; tetra-n-propyl titanate; tetra-n-butyl titanate; tetraisooctyltitanate; tetraisostearoyl titanate; tetraoctyleneglycol titanate;ethoxybis(pentane-2,4-dionato-0,0′)propan-2-olato)titanium and titaniumtetrabutanolate polymer. Most preferably the organo-titante is atitanium tetrabutanolate polymer (e.g., Tyzor® BTP available fromDuPont).

Preferably, the curable liquid polysiloxane/TiO₂ composite of thepresent invention has a purity of ≧95 wt % (more preferably ≧98 wt %).Preferably, the raw materials used in the preparation of the curableliquid polysiloxane/TiO₂ composite of the present invention are purifiedto enhance the purity of the curable liquid polysiloxane/TiO₂ compositeproduct. The raw materials used can be purified by, for example,distillation, chromatography, solvent extraction, membrane separationand other well known purification processes.

The curable liquid polysiloxane/TiO₂ composite optionally furthercomprise an additive selected from the group consisting of inertdiluents; reactive diluents; hindered amine light stabilizers (HALS);lubricity additives; fungicides; flame retardants; contrast enhancers;UV-stabilizers; photostabilizers; surfactants; adhesive modifiers;rheology modifiers; phosphors; absorbing dyes; fluorescent dyes;electrical or thermal conductivity additives; chelating or sequestratingagents; acid scavengers; base scavengers; metal passivators; and metalfortifiers.

The light emitting diode manufacturing assembly of the presentinvention, comprises: a support structure having a plurality ofindividual semiconductor light emitting diode dies; and, a mold having aplurality of cavities corresponding with the plurality of individualsemiconductor light emitting diode dies; wherein the plurality ofcavities is filled with a curable liquid polysiloxane/TiO₂ composite ofthe present invention; and wherein the support structure and the moldare oriented such that the plurality of individual semiconductor lightemitting diode dies are each at least partially immersed in the curableliquid polysiloxane/TiO₂ composite contained in the plurality ofcavities. Preferably, each of the cavities in the plurality of cavitiesare in the shape of a lens. Preferably, the curable liquidpolysiloxane/TiO₂ composite is heat curable (more preferably, whereinthe curable liquid polysiloxane/TiO₂ composite is cured upon heating at100 to 200° C. for 10 to 120 minutes). Preferably, the curable liquidpolysiloxane/TiO₂ composite when cured both encapsulates the individualsemiconductor light emitting diode dies and functions as a lens. Themold optionally further comprises a plurality of feed channels thatfacilitate injection of the curable liquid polysiloxane/TiO₂ compositeinto the plurality of cavities.

The light emitting diode manufacturing assembly of the present inventionfacilitates the manufacture of designed manifolds containing multipleindividual semiconductor light emitting dies for use in, for example,automobile headlight assemblies. Alternatively, the light emitting diodemanufacturing assembly of the present invention facilitates themanufacture of individual semiconductor light emitting diodes. That is,upon curing of the curable liquid polysiloxane/TiO₂ composite, the moldcan then be separated from the assembly and the plurality of individualsemiconductor light emitting diode dies encapsulated by the curedcurable polysiloxane/TiO₂ composite on the substrate can be diced intomultiple individual semiconductor light emitting diodes.

Some embodiments of the present invention will now be described indetail in the following Examples.

Siloxane monomer having the structural formula

is referred to in the following examples as “POP”. The POP monomer usedin the following examples was prepared according to the basic proceduredescribed in Example 1.

Siloxane monomer having the structural formula

is referred to in the following examples as PTMS and is commerciallyavailable from Gelest Inc.

Example 1 POP Monomer Preparation

A 500 mL Schlenk flask was charged with diethyl ether (400 mL);magnesium metal powder (3.3 g; 135 mmol); and methyl iodide (0.1 mL).The flask was then further charged with 4-bromodiphenyl ether (32.161 g;129 mmol) and the reaction mixture was stirred for 4 hours.Phenyltrimethoxysilane (25.601 g, 129 mmol) was then added to the flaskand the contents were then stirred for an additional hour. The contentsof the flask were then transferred to a 1 L separatory funnel and thematerial was washed twice with 400 mL of distilled water. The etherlayer was collected and the volatiles were removed under reducedpressure. The purity of the crude product was further purified by shortpath distillation to a product POP monomer having a purity of ≧97%. Theproduct POP monomer contained ≦500 ppm phenoxyphenyl halide.

Comparative Example A and Examples 2-4 Preparation of Curable LiquidPolysiloxane/TiO₂ Composites

Curable liquid polysiloxane/TiO₂ composites were prepared using thefollowing general procedure using the specific amounts noted in TABLE 1.Specifically, the POP and PTMS in the amounts noted in TABLE 1 wereadded with 13.2 g of propylene glycol methyl ether acetate (PGMEA) a 100mL three-neck round bottom flask. A solution of 5.0 g methanol, 1.0 gwater and 0.16 g concentrated hydrochloric acid (37% in water, fromFisher Scientific) was then added to the flask drop wise. The contentsof the flask were then heated to 70° C. and maintained at thattemperature with a constant temperature heating mantle with a thermalprobe and reflux condenser for 1.5 hours. Titanium tetrabutanolatepolymer (available from DuPont as Tyzor® BTP) in the amount noted inTABLE 1 dissolved in 8.8 g of PGMEA and 1 mL of dry tetrahydrofuran(THF) was then added to the flask drop wise through an addition funnelwhile maintaining the temperature of the flask contents at 70° C. for 1hour. Water (0.1 mL) and PGMEA (4.4 g) were then added to the flask. Thecontents of the flask were then heated to 100° C. and allowed to reactfor 1 hour. The volatiles were then distilled out of the flask with ashort path distillation column. Volatiles were then further eliminatedfrom the flask contents by roto-evaporation followed by the pulling of ahigh vacuum (25 mTorr) at 60° C. The product optically clear, curableliquid polysiloxane/TiO₂ composite of Examples 2-4 was then recoveredfrom the flask. Note that the reaction described in Comparative ExampleA yielded a milky white two phase mixture, indicating the formation andaggregation of colloidal TiO₂ particles.

TABLE 1 Tyzor ® POP PTMS TiO₂ POP PTMS BPT (in (in (in Ex. # (in g) (ing) (in g) mol %)^(ζ) mol %)^(ζ) mol %)

A 3.4 0.106 5.45 95 5 67 2 5.9 0.212 4.54 94 6 49.1 3 5.9 0.212 5.45 946 53.7 4 3.4 0.106 0.83 95 5 23.6 ^(ζ)based on total moles of siloxanemonomers (POP + PTMS)

based on total combined moles of both siloxane monomers (POP + PTMS) andthe equivalent molar amount of TiO₂ introduced by Tyzor ® BPTincorporation (i.e., three moles of TiO₂ for each mole of Tyzor ® BPT)

Comparative Example B and Examples 5-8 Preparation of Curable LiquidPolysiloxane/TiO₂ Composites

Curable liquid polysiloxane/TiO₂ composites were prepared using thefollowing general procedure using the specific amounts noted in TABLE 2.Specifically, the POP and PTMS in the amounts noted in TABLE 2 wereadded with 6.6 g of propylene glycol methyl ether acetate (PGMEA) a 100mL three-neck round bottom flask. A solution of 2.5 g methanol, 0.5 gwater and 0.08 g concentrated hydrochloric acid (37% in water, fromFisher Scientific) was then added to the flask drop wise. The contentsof the flask were then heated to 70° C. and maintained at thattemperature with a constant temperature heating mantle with a thermalprobe and reflux condenser for 1.5 hours. Titanium tetrabutanolatepolymer (available from DuPont as Tyzor® BTP) in the amount noted inTABLE 2 dissolved in 4.4 g of PGMEA and 0.5 mL of dry tetrahydrofuran(THF) was then added to the flask drop wise through an addition funnelwhile maintaining the temperature of the flask contents at 70° C. for 1hour. Water (0.05 mL) and PGMEA (2.2 g) were then added to the flask.The contents of the flask were then heated to 100° C. and allowed toreact for 1 hour. The volatiles were then distilled out of the flaskwith a short path distillation column. Volatiles were then furthereliminated from the flask contents by roto-evaporation followed by thepulling of a high vacuum (25 mTorr) at 60° C. The product opticallyclear, curable liquid polysiloxane/TiO₂ composite was then recoveredfrom the flask.

TABLE 2 Tyzor ® POP PTMS TiO₂ POP PTMS BPT (in (in (in Ex. # (in g) (ing) (in g) mol %)^(ζ) mol %)^(ζ) mol %)

B 2.9 0.085 0 95 5 0 5 2.9 0.106 1.36 94 6 37 6 2.95 0.018 2.63 99 1 547 2.9 0.02 0.7 99 1 24 8 3.1 0.21 3.05 90 10 24 ^(ζ)based on total molesof siloxane monomers (POP + PTMS)

based on total combined moles of both siloxane monomers (POP + PTMS) andthe equivalent molar amount of TiO₂ introduced by Tyzor ® BPTincorporation (i.e., three moles of TiO₂ for each mole of Tyzor ® BPT)

Examples 9-12 Preparation of Curable Liquid Polysiloxane/TiO₂ Composites

Curable liquid polysiloxane/TiO₂ composites were prepared using thefollowing general procedure using the specific amounts noted in TABLE 3.Specifically, the POP and PTMS in the amounts noted in TABLE 3 wereadded with 15 mL of propylene glycol methyl ether acetate (PGMEA) a 100mL three-neck round bottom flask. A solution of 5 g methanol, 1 g waterand 0.16 g concentrated hydrochloric acid (37% in water, from FisherScientific) was then added to the flask drop wise. The contents of theflask were then heated to 70° C. and maintained at that temperature witha constant temperature heating mantle with a thermal probe and refluxcondenser for 1.5 hours. Titanium tetrabutanolate polymer (availablefrom DuPont as Tyzor® BTP) in the amount noted in TABLE 3 dissolved in10 mL of PGMEA and 1 mL of dry tetrahydrofuran (THF) was then added tothe flask drop wise through an addition funnel while maintaining thetemperature of the flask contents at 70° C. for 1 hour. Water (0.1 mL)and PGMEA (5 mL) were then added to the flask. The contents of the flaskwere then heated to 100° C. and allowed to react for 1 hour. Volatileswere then further eliminated from the flask contents by roto-evaporationunder a high vacuum at 60° C. The product optically clear, curableliquid polysiloxane/TiO₂ composite was then recovered from the flask.

TABLE 3 Tyzor ® POP PTMS TiO₂ POP PTMS BPT (in (in (in Ex. # (in g) (ing) (in g) mol %)^(ζ) mol %)^(ζ) mol %)

9 5.907 0.0035^(†) 5.465 99.9 0.1 55.3 10 5.911 0.0175 5.450 99.5 0.555.0 11 5.902 0.108 5.472 97.0 3.0 54.6 12 5.905 0.224 5.460 94.0 6.053.7 ^(†)4.7 μL of PTMS material was added to the solution, which amountcontained about 0.0035 g of the monomer. ^(ζ)based on total moles ofsiloxane monomers (POP + PTMS)

based on total combined moles of both siloxane monomers (POP + PTMS) andthe equivalent molar amount of TiO₂ introduced by Tyzor ® BPTincorporation (i.e., three moles of TiO₂ for each mole of Tyzor ® BPT)

Comparative Examples C-D

Composites were prepared using the following general procedure using thespecific amounts noted in TABLE 4. Specifically, POP monomer in theamount noted in TABLE 4 was added with 6.6 g of propylene glycol methylether acetate (PGMEA) a 100 mL three-neck round bottom flask. A solutionof 2.5 g methanol, 0.5 g water and 0.08 g concentrated hydrochloric acid(37% in water, from Fisher Scientific) was then added to the flask dropwise. The contents of the flask were then heated to 70° C. andmaintained at that temperature with a constant temperature heatingmantle with a thermal probe and reflux condenser for 1.5 hours. Titaniumtetrabutanolate polymer (available from DuPont as Tyzor® BTP) in theamount noted in TABLE 4 dissolved in 4.4 g of PGMEA and 0.5 mL of drytetrahydrofuran (THF) was then added to the flask drop wise through anaddition funnel while maintaining the temperature of the flask contentsat 70° C. for 1 hour. Water (0.05 mL) and PGMEA (2.2 g) were then addedto the flask. The contents of the flask were then heated to 100° C. andallowed to react for 1 hour. The product obtained in each of ComparativeExamples C and D was milky white and completely opaque, indicating theformation and aggregation of colloidal TiO₂ particles.

TABLE 4 POP Tyzor ® TiO₂ Ex. # in g BPT in g (in mol % )

C 2.9 0.7 24.4 D 2.9 2.6 54.5

based on moles of POP and the equivalent molar amount of TiO₂ introducedby Tyzor ® BPT incorporation (i.e.,three moles of TiO₂ for each mole ofTyzor ® BPT)

Comparative Example E One Step Preparation

POP (2.9 g) and PTMS (0.09 g) dissolved in 6.6 grams of propylene glycolmethyl ether acetate (PGMEA), and Tyzor® BTP (0.72 g) dissolved in 4.4 gof PGMEA and 0.5 mL of dry tetrahydrofuran (THF) were charged to a 100mL round bottom flask. A solution of 2.5 g methanol, 0.5 g water and0.08 g concentrated hydrochloric acid (37% in water, from FisherScientific) was then added to the flask drop wise. The contents of theflask were then heated to 70° C. and maintained at that temperature witha constant temperature heating mantle with a thermal probe and refluxcondenser for 1.5 hours. The resulting product was milky white andcompletely opaque, indicating the formation and aggregation of colloidalTiO₂ particles.

Comparative Examples VA and VC-VE, and Examples V2-V11

The viscosity of each of the products from Comparative Examples A andC-E and Examples 2-11 was assessed in Comparative Examples VA and VC-VE,and Examples V2-V11, respectively, using the following general procedureusing a Rheometrics Mechanical Spectrometer (RMS-800) made by RheometricScientific Inc. (currently TA Instruments, New Castle, Del.).Specifically, in each instance a sample of the material to be tested wasloaded and sandwiched between two aluminum parallel plates of 8 mmdiameter. The rheometer fixtures and plates were preheated to 60° C. andequilibrated at this temperature for 15 minutes before zeroing the gapbetween the plates. The temperature of the parallel plates was thenincreased to 90° C. for liquid samples having viscosities greater than100 Pa-s to facilitate the sample loading. After loading the samplematerial onto the bottom plate, the instrument was placed on HOLD untilthe oven cooled back to 60° C. The sample gap was then adjusted to 0.5mm. Extra sample loaded onto the bottom plate that was squeezed out tothe edge of the parallel plates during the gap setting was trimmed awayusing a spatula. The sample gap was then recorded from the instrumentmicrometer once the temperature reached equilibrium (after about 15min). A dynamic frequency sweep was then commenced from 100 rad/s to 0.1rad/s at a strain level within the linear viscoelastic range. Thecomplex shear viscosity was recorded as a function of frequency. Theviscosity data at 60° C. and 10 rad/s is reported in TABLE 5 to indicatethe relative ease with which each sample material flowed.

TABLE 5 Ex. Material Tested Viscosity (in Pa's) VA Product of A solid VCProduct of C not measured (NM), Product of C was two phase VD Product ofD NM, Product of D was two phase VE Product of E NM, Product of E wastwo phase V2 Product of Ex. 2 8.1 × 10⁴ V3 Product of Ex. 3 5.2 × 10⁵ V4Product of Ex. 4 4.2 V5 Product of Ex. 5 1.4 × 10² V6 Product of Ex. 61.4 × 10³ V7 Product of Ex. 7 7.8 V8 Product of Ex. 8 29 V9 Product ofEx. 9 6.8 × 10⁴ V10 Product of Ex. 10 1.1 × 10⁴ V11 Product of Ex. 118.2 × 10³

Comparative Example RB and Examples R2-R12 Refractive Indexes

The refractive index of the products from Comparative Example B andExamples 2-12 were determined by visual observation in ComparativeExample RB and Examples R2-R12, respectively, using an Atago DigitalRefractometer (Model: RX-7000α) at sodium D-line. The results arereported in TABLE 6.

TABLE 6 Ex. Material Tested RI (at 589 nm) RB Product of B 1.608 R2Product of Ex. 2 1.641 R3 Product of Ex. 3 1.650 R4 Product of Ex. 41.621 R5 Product of Ex. 5 1.637 R6 Product of Ex. 6 1.648 R7 Product ofEx. 7 1.632 R8 Product of Ex. 8 1.635 R9 Product of Ex. 9 1.651 R10Product of Ex. 10 1.648 R11 Product of Ex. 11 1.650 R12 Product of Ex.12 1.650

Example S3

The average TiO₂ domain size in the curable liquid polysiloxane/TiO₂composite prepared according to Example 3 was determined to be about 3nm by transmission electron microscopy (TEM) using a JEOL 2010F fieldemission transmission electron microscope operating at 200 keV andequipped with a Bruker XFlash® 5030 SDD silicon drift energy dispersivex-ray detector.

Example S9

The average TiO₂ domain size in the curable liquid polysiloxane/TiO₂composite prepared according to Example 9 was determined to be <5 nmwith a JEOL JEM 1230 transmission electron microscopy operated at a 100kV accelerating voltage, using Gatan 791 and Gatan 794 digital camerasto capture the bright field images at −70° C. and post processing theimages using Adobe Photoshop 7.0.

Examples C₉-C₁₂

In Examples C₉-C₁₂ a sample of the curable liquid polysiloxane/TiO₂composite prepared according to each of Examples 9-12, respectively, wasthermally cured. In each of Examples C₉-C₁₂ a sample of the curableliquid polysiloxane/TiO₂ composite material was placed in a convectionoven set at 120° C. for one hour. In each of Examples C₉-C₁₂, theinitially liquid composite material was fully cured into a rigid solidfollowing the thermal treatment in the convection oven.

1. A curable liquid polysiloxane/TiO₂ composite for use as a lightemitting diode encapsulant, comprising: a polysiloxane prepolymer withTiO₂ domains having an average domain size of less than 5 nm; whereinthe polysiloxane prepolymer has an average compositional formula:(R⁴ ₃SiO_(1/2))_(a)(R¹(R²)SiO_(2/2))_(b)(R³SiO_(3/2))_(c)(R⁵_(x)Z_(y)SiO_((4-x-y)/2))_(d) wherein each R¹ and R³ is independentlyselected from a C₆₋₁₀ aryl group and a C₇₋₂₀ alkylaryl group; whereineach R² is a phenoxyphenyl group; wherein each R⁴ is independentlyselected from a C₁₋₁₀ alkyl group, a C₇₋₁₀ arylalkyl group, a C₇₋₁₀alkylaryl group and a C₆₋₁₀ aryl group; wherein each R⁵ is independentlyselected from a C₁₋₁₀ alkyl group, a C₇₋₁₀ arylalkyl group, a C₇₋₁₀alkylaryl group, a C₆₋₁₀ aryl group and a phenoxyphenyl group; whereineach Z is independently selected from a hydroxyl group and a C₁₋₁₀alkoxy group; wherein 0≦a≦0.005; wherein 0.8495≦b≦0.9995; wherein0.0005≦c≦0.10; wherein 0≦d≦0.15; wherein the curable liquidpolysiloxane/TiO₂ composite contains 20 to 60 mol % TiO₂ (based on totalsolids); wherein each x is independently selected from 0, 1 and 2;wherein each y is independently selected from 1, 2 and 3; whereina+b+c+d=1; and, wherein the curable liquid polysiloxane/TiO₂ compositeexhibits a refractive index of >1.61 to 1.7 and wherein the curableliquid polysiloxane/TiO₂ composite is a liquid at room temperature andatmospheric pressure.
 2. The curable liquid polysiloxane/TiO₂ compositeof claim 1, wherein the curable liquid polysiloxane/TiO₂ composite isprepared by: (a) combining in an aprotic solvent: (i) D units having aformula R¹(R²)Si(OR⁶)₂; (ii) T units having a formula R³Si(OR⁷)₃; (iii)optionally, M units having a formula R⁴ ₃SiOR⁸; and, (iv) optionally, Qunits having a formula S1(OR⁹)₄; wherein each R⁶, R⁷, R⁸ and R⁹ isindependently selected from a hydrogen atom, a C₁₋₁₀ alkyl group, aC₇₋₁₀ arylalkyl group, a C₇₋₁₀ alkylaryl group and a C₆₋₁₀ aryl group;(b) adding to the combination of (a) an acid in a miscible mixture ofwater and an alcohol to form a reaction mixture; (c) allowing thereaction mixture to react; (d) adding an organo-titanate in an aproticsolvent to the reacted reaction mixture of (c); (e) adding water to theproduct of (d); (f) heating the product of (e) and allowing it to react;and, (g) purifying the product of (f) to provide the curable liquidpolysiloxane/TiO₂ composite.
 3. The curable liquid polysiloxane/TiO₂composite of claim 2, wherein the curable liquid polysiloxane/TiO₂composite provided has a purity of ≧95 wt %.
 4. The curable liquidpolysiloxane/TiO₂ composite of claim 3, wherein the D units have aformula

wherein each R⁶ is independently selected from hydrogen and a C₁₋₄ alkylgroup.
 5. The curable liquid polysiloxane/TiO₂ composite of claim 4,wherein each R⁶ is a methyl group.
 6. The curable liquidpolysiloxane/TiO₂ composite of claim 4, wherein the T units have aformula

wherein each R⁷ is independently selected from hydrogen and a C₁₋₄ alkylgroup.
 7. The curable liquid polysiloxane/TiO₂ composite of claim 6,wherein each R⁷ is a methyl group.
 8. A light emitting diodemanufacturing assembly, comprising: a support structure having aplurality of individual semiconductor light emitting diode dies; and, amold having a plurality of cavities corresponding with the plurality ofindividual semiconductor light emitting diode dies; wherein theplurality of cavities is filled with a curable liquid polysiloxane/TiO₂composite of claim 1; and wherein the support structure and the mold areoriented such that the plurality of individual semiconductor lightemitting diode dies are each at least partially immersed in the curableliquid polysiloxane/TiO₂ composite contained in the plurality ofcavities.
 9. The light emitting diode manufacturing assembly of claim 8,wherein the cavities are in the shape of lenses.
 10. The light emittingdiode manufacturing assembly of claim 8, wherein the mold furthercomprises a plurality of feed channels that facilitate injection of thecurable liquid polysiloxane/TiO₂ composite into the plurality ofcavities.